Humus – the end result of composting – is also what happens naturally on the forest floor with the breakdown of leaf litter, flowers etc. It’s the organic matter that is needed in soil to provide nutrients and to unlock minerals in the soil particles. It also creates the structure in soil that is vital for water and oxygen flow, without which the soil becomes so compact that plant roots cannot penetrate far, resulting in poor plant health. When we add compost to our soil we are also adding millions of microbes that then ‘inoculate’ the soil with active populations to keep the soil alive and working.

Gardeners can keep composting very simple or become more directly involved and create some amazing soil additives that provide incredible results in the garden. I see composting as a form of creation, alchemy even, where through the natural break down of humble organic materials – and a little human care – we end up with something far more than the sum of its parts – a gardener’s form of gold.

There are many different types of composting; depending on how much space, time and energy you can give to the process, but all types will create a beneficial product for your soil.

A pile of lawn clippings in the back corner of your yard will break down in time and be valuable for your soil.

There are a number of retail bins on the market designed to be filled gradually that will contain the pile and keep it tidy. The end product can be harvested from the base of the bin while the top is still composting. These are great for producing small amounts gradually. This style of composting is called cold composting and usually becomes a large worm farm, also a fantastic way of breaking down organic matter.

Tumblers are plastic bins on legs with a handle to make turning easy, these are also an effective method of composting. Adding a handful of soil or compost to kick-start the microbe life in the tumbler is helpful.

Hot composting is the method we use at the Yarra Valley Living Centre because of the superior result; it does however require more space, time and energy. The heaps are made from start to finish in one day and then left to do their thing. Bays to hold the piles can be made from many materials, we are currently using star pickets and chicken wire as a cheap and quick way of creating on the go, using bays of 1.5 cubic metres.

The work in all compost piles is done by microbes – bacteria and fungi that do the ‘breaking down’ for us. Our job as composters is to provide the ideal conditions for the right microbes to thrive, and to do this we need to provide a balance of nitrogen and carbon based ingredients.

Nitrogen based ingredients are the green and fresh things like fresh grass clippings, animal manure, weeds and kitchen scraps.

Carbon based ingredients are the brown and dry things like straw, hay, leaves, cardboard and paper.

We use roughly a 50/50 ratio. All ingredients have their own blend of nitrogen and carbon so we find a rough mix of half fresh and half dry works. We build the pile with thin layers (approx. 10-20 cm) of wet/dry ingredients and find the heap looks after itself best if the layers are kept thin.

To do their work efficiently, microbes need moisture and oxygen, so our job is to make sure the heap is damp and has spaces for air pockets. A mix of particle sizes within a heap takes care of air pockets, often we will put twigs and sticks in as part of the pile and while they may not break down completely they are performing an important role. Corncobs and other larger kitchen scraps fulfil the same role in the compost heap. When using our compost, whatever hasn’t broken down yet just gets put into the next pile.

When the ingredients in the heap start to break down, the microbes use the nitrogen as fuel to digest the carbon and warmth is created which heats up the whole heap. Ideally the compost would get between 55 and 75 degrees Celsius, to kill any weed seeds and pathogens from the ingredients, but is not essential. To reach these heat levels a pile of 1 metre cubed minimum is necessary. The bulk of the work done within a compost heap is during the warm-phase; the microbes responsible for this warming are dependent on the moisture and air within the soil. If the ideal conditions are not present, a different family of microbes will flourish – the anaerobic microbes. These will still do the work, however there will be an unpleasant smell and it will take a lot longer to fully break down. To remedy this usually turning, fluffing up and introducing air will rebalance the microbes. Sometimes extra carbon added would help with a pile that is too wet and stinky.

Having small particles in the mix helps to speed up the warming and ‘cooking’ process of a heap so using a mower to break down green bulky is something worth considering.

Diversity of ingredients is important; each ingredient adds its own unique blend of minerals and nutrients and contributes to a more balanced end product.

We have found with enough small particles and thin layers some of our composts have not needed turning at all, and after 4 to 6 months are beautiful and sweet smelling.

The heap drops down in volume and ends up being roughly one third of the original size and very dense.

Composting is not an exact science; there are no rules only guidelines. Enjoy the process, and enjoy being a co-creator in the garden.